The present invention relates to method and apparatus for displaying a road map in a form of bird""s eye view.
The present invention is applicable to apparatus for navigating a vehicle to a destination using a display unit.
A Japanese Patent Application First Publication No. Heisei 7-190791 exemplifies a previously proposed apparatus for executing a coordinate transformation of a plan view formed road map piece (mesh) into a bird""s eye view (perspectively projected view).
However, since the previously proposed apparatus executes the coordinate transformation even if a scrolling operation for a display screen is carried out, a processor capable of processing a large amount of data (a processor having a high processing capability) is required in order to maintain a scrolling velocity to some degree. This causes an increase in a total cost of assembling the whose apparatus.
It is an object of the present invention to provide method and apparatus for displaying a road map mesh in a form of bird""s eye view on a display screen of a display unit without use of a processor having a high processing capability and at a high drawing velocity of the bird""s eye view.
The above-described object can be achieved by providing a method for displaying a road map mesh in a form of bird""s eye view on a display screen of a display unit, comprising:
a) storing the road map mesh in a form of a plan view;
b) placing a virtual viewpoint at an upper sky behind a predetermined position of display reference on the plan view formed road map mesh by a predetermined distance;
c) looking down at the plan view formed road map mesh forward away from the predetermined point of display reference from said virtual viewpoint along a line of sight having an angle of field of view with respect to the predetermined point of display reference;
d) setting the display screen on a plane perpendicular to the line of sight;
e) extracting road map data from the plane view formed road map mesh corresponding to respective pixels on the display screen from the plan view formed road map mesh; and,
f) drawing the bird""s eye view of the plan view formed road map mesh on the display screen on the basis of the extracted road map data.
The above-described object can also be achieved by providing an apparatus for displaying a road map mesh in a form of bird""s eye view on a display screen of a display unit, comprising:
a memory arranged for storing the road map mesh in a form of a plan view; and
a picture drawing processor arranged for placing a virtual viewpoint at an upper sky behind a predetermined point of display reference by a predetermined distance, looking down at the plan view formed road map mesh forward away from the predetermined point of display reference from said virtual viewpoint along a line of sight having an angle of field of view with respect to the predetermined point of display reference, setting the display screen on a plane perpendicular to the line of sight, extracting road map data on the plan view formed map mesh corresponding to respective pixles on the display screen from the plan view formed road map mesh, and drawing the bird""s eye view of the plan view formed road map mesh on the display screen on the basis of the extracted road map data.